1. Field of the Invention
The present invention relates generally to semiconductor lasers, and more particularly to semiconductor lasers of the vertical-cavity surface-emitting type.
2. Description of the Related Art
Semiconductor light-emitting devices such as semiconductor lasers, semiconductor light-emitting diodes, etc., are widely used not only in the optical communication field, but also in the consumer field and the commercial field represented by optical disk systems using CD (Compact Disc), DVD (Digital Versatile Disc), etc., or by barcode readers, etc.
Of these semiconductor light-emitting devices, a vertical-cavity surface-emitting laser configures an optical cavity structure using an active layer sandwiched between a pair of mirror stack and emits a laser beam perpendicularly to a surface of semiconductor substrate.
Since the vertical-cavity surface-emitting laser enables two-dimensional integration of various laser devices on the substrate, much attention is focused on the vertical-cavity surface-emitting laser as a key device for high-speed LAN (Local Area Network), optical interconnects, etc., in the optoelectronics field.
The vertical-cavity surface-emitting laser is featured as follows.
Compared to an edge-emitting semiconductor laser, for example, the vertical-cavity surface-emitting laser has many advantages such as a low threshold current operation, low power consumption, high luminescence efficiency, capable of high-speed modulation, a small beam divergence for easy connection to an optical fiber, requiring no edge cleavage, excellent for mass production, etc.
In addition to these features, the vertical-cavity surface-emitting laser is optimal as an optical source for high-speed optical links. In combination with plastic optical fibers, it is expected to provide an optical source for high-speed optical links at low prices. Research and development is conducted extensively for this purpose.
The vertical-cavity surface-emitting laser requires a current confinement portion for efficiently injecting electric currents into an active region. A method for forming the current confinement portion is to form a high-resistance region by means of proton implantation and define a current aperture. However, this method requires complicated manufacturing processes, thus increasing costs.
Another method proposed is to form a laser structure comprising a layer to be oxidized which includes a high-Al content layer (AlGaAs layer, for example), etch the layer in a mesa, selectively and laterally oxide the layer to be oxidized from a side face of the mesa (lateral selective oxidation), and use a non-oxidized region as a current aperture. However, this method causes problems such that interconnection breakage occurs due to a step formed between the mesa and the peripheral portion thereof, and oxidation of the layer to be oxidized which includes the high-Al content layer involves volume shrinkage thereof, with result that stress is induced in the mesa.
It has been long expected to provide a highly reliable semiconductor surface light-emitting device that can be manufactured with a simple process and to provide a method for manufacturing thereof.
A semiconductor light-emitting device which emits the light vertical to a top surface, according to a first aspect of the invention comprises:
a substrate having a first principal surface and a second principal surface;
a first electrode formed on the first principal surface of the substrate;
a multi-layered structure having a light-emitting part, a groove, and a peripheral part which is formed on the second principal surface of the substrate;
the light-emitting part of a column shape substantially surrounded by the groove extending from a surface of the multi-layered structure and substantially isolated from the peripheral part by the groove, the groove having deeper portions and shallower portions alternately arranged, the light-emitting part comprising:
a first multi-layered reflecting mirror layer formed on the first principal surface of the substrate, the deeper portions of the groove extending into the first multi-layered reflecting mirror layer;
a semiconductor active layer formed above the first multi-layered reflecting mirror layer;
a second multi-layered reflecting mirror layer formed above the semiconductor active layer; and
a current confinement path defined and surrounded by an oxidized region of at least one of the first and second multi-layered reflecting mirror layers, the shallower portions of the groove extending to the oxidized region;
the peripheral part of the multi-layered structure surrounding the light-emitting part via the groove;
a second electrode formed on the top surface of the light-emitting part and having an opening formed above the current confinement path, the second electrode being configured to make a current path to the first electrode through the current confinement path;
a third electrode for external connection formed on the peripheral part of the multi-layered structure; and
interconnection conductors bridging between the second and third electrodes to establish electrical connections above the shallower portions of the groove, respectively.
A semiconductor light-emitting device which emits the light vertical to a top surface, according to a second aspect of the invention comprises:
a substrate having a first principal surface and a second principal surface;
a first electrode formed on the first principal surface of the substrate;
a multi-layered structure having a light-emitting part, grooves, and a peripheral part which is formed on the second principal surface of the substrate;
the light-emitting part of a column shape substantially surrounded by the grooves extending from a surface the multi-layered structure and partially connected to the peripheral part at high resistance connecting portions between opposing ends of adjacent ones of the grooves, the light-emitting part comprising;
a first multi-layered reflecting mirror layer formed on the first principal surface of the substrate, the grooves extending into the first multi-layered reflecting mirror layer;
a semiconductor active layer formed above the first multi-layered reflecting mirror layer;
a second multi-layered reflecting mirror layer formed above the semiconductor active layer; and
a current confinement path defined and surrounded by an oxidized region of at least one of the first and second multi-layered reflecting mirror layers;
the peripheral part of the multi-layered structure surrounding the light-emitting part via the grooves; and
a second electrode formed on the top surface of the light-emitting part and having an opening formed above the current confinement path, the second electrode being configured to make a current path to the first electrode through the current confinement path;
a third electrode for external connection formed on the peripheral part of the multi-layered structure; and
interconnection conductors formed on the connecting portions and connecting the second electrode with the third electrode.
A semiconductor light-emitting device which emits the light vertical to a top surface, according to a third aspect of the invention comprises:
a substrate having a first principal surface and a second principal surface;
a first electrode formed on the first principal surface of the substrate;
a multi-layered structure having a light-emitting part, grooves, and a peripheral part which is formed on the second principal surface of the substrate;
the light-emitting part of a column shape substantially surrounded by the grooves extending from a surface of the multi-layered structure and partially connected to the peripheral part at high resistance connecting portions between opposing ends of adjacent ones of the grooves, the light-emitting part comprising:
a first multi-layered reflecting mirror layer formed on the first principal surface of the substrate, the grooves extending into the first multi-layered reflecting mirror layer;
a semiconductor active layer formed above the first multi-layered reflecting mirror layer;
a second multi-layered reflecting mirror layer formed above the semiconductor active layer; and
a current confinement path defined and surrounded by an oxidized region of at least one of the first and second multi-layered reflecting mirror layers, and the oxidized region having oxidation anisotropy providing a first direction of a high oxidation rate and a second direction of low oxidation rate with respect to a crystal orientation of the first multi-layered reflecting mirror layer or the second multi-layered reflecting mirror layer, a distance from a side of the light-emitting part to the current confinement path in the first direction being longer than a distance from a side of the light-emitting part to the light-emitting region in the second direction;
the peripheral part of the multi-layered structure surrounding the light-emitting part via the grooves; and
a second electrode formed on the top surface of the light-emitting part and having an opening formed above the current confinement path, the second electrode being configured to make a current path to the first electrode through the current confinement path;
a third electrode for external connection formed on the peripheral part of the multi-layered structure; and
interconnection conductors formed on the connecting portions and connecting the second electrode with the third electrode.
A semiconductor light-emitting device according to a fourth aspect of the invention has the same configuration as that of the light-emitting device according to the third aspect, wherein the oxidized region of the current confinement path has oxidation anisotropy providing a first direction of a high oxidation rate and a second direction of low oxidation rate with respect to a crystal orientation of the first multi-layered reflecting mirror layer or the second multi-layered reflecting mirror layer, and the first direction is directed to the high resistance connecting portions.